1. Field of the Invention
The present invention relates to improvements in the construction and manufacture of polymeric bags. In particular, the present invention relates to improvements applicable to drawstring trash bags.
2. Description of the Related Art
Polymeric bags are ubiquitous in modern society, available in various capacities, thicknesses, dimensions and colors. Polymeric bags are utilized in a variety of ways including typical consumer applications such as long-term storage, food storage, and trash collection. As with many other consumer products, increased demand and new technology have resulted in innovations in the utility and performance of polymeric bags. The present invention is an innovation of particular relevance to polymeric bags used for trash collection.
Polymeric bags are manufactured from the polymeric film produced using one of several thin-film manufacturing processes known in the art, the two most common being the blown-film extrusion process and the cast-film extrusion process. Blown-film extrusion and cast-film extrusion each offer specific advantages over the other method. Consequently, the ultimate determination of the preferred manufacturing method for each specific thin-film product application is driven by considerations that may include desired film properties and advantages in cost or manufacturing speed.
For blown-film extrusion and cast-film extrusion, an extruder is used to push molten polymeric material through a die, producing a tubular film in the blown-film extrusion process or a substantially flat film in the cast-film extrusion process. Technological innovations have improved both of these manufacturing processes over the past several decades with new improvements continually being developed. Examples of such innovations include development of multi-layer dies as described in U.S. Pat. No. 4,185,954 entitled Die for Extruding Tubes Composed of Plurality of Layers and improved air cooling systems as described in U.S. Pat. No. 7,753,666 entitled Apparatus and Method for Cooling Plastic Film Tube in Blown Film Process.
One specific application of a plastic thin-film manufacturing process is in the production and conversion of plastic trash bags. Several types of trash bags are available, but drawstring trash bags are one of the popular styles of plastic trash bags, if not the most popular. Drawstring trash bags feature a hem or, more typically a pair of hems, extending along the top of the trash bag with a drawstring disposed within each hem. When using drawstring trash bags, consumers typically pull the drawstrings to close the top of the bag and subsequently tie the drawstrings together to secure the bag contents within the bag. The drawstrings also provide a convenient carry handle for transporting the filled bag.
In the prior art, it is known to provide additional strength for the drawstring. In particular, for many years drawstrings have been made with stronger and thicker materials than the body of the bag. Specifically, it has long been known in the prior art to use high-density polyethylene (HDPE) as the primary material for the drawstrings as compared to low density polyethylene (LDPE) or linear low density polyethylene (LLDPE) used for the body of the bag due to the increased stiffness and tensile strength offered by high density polyethylene. Drawstrings have also been historically thicker than the body of the drawstring trash bag to provide increased strength. For example, most drawstring trash bags are constructed with drawstrings having a thickness of 2.25 to 3 mils and a bag body thickness of between 0.7 mils and 1.2 mils. Other innovations include multilayered drawstrings for improved strength and sealing characteristics as described in U.S. Pat. No. 5,006,380. Other strategies known in the prior art include the inclusion of newer, more sophisticated materials or the use of machine direction orientation (MDO) processes. To date, however, improvements to drawstring trash bags have focused primarily on improving the performance of the drawstrings or on modifying the drawstrings in efforts to make them more compatible with the bag body. And, little to no consideration has been given improving the bag body—most specifically the hem areas—to make it more compatible with the drawstring during use. In particular, little to no attention has been paid to the area of the drawstring trash bags where the hems and hem seals are located and the area immediately surround such hem seals.
With the advent of stronger drawstrings as described above, consumers are prone to heavily load drawstring trash bags. The increased weight of the contents placed in the bags puts additional strain on the drawstring trash bag when a consumer pulls the drawstring trash bag out of a receptacle or uses the drawstrings to carry the loaded drawstring trash bag. While the stronger drawstrings developed over the years are increasingly suitable for handling such increased loads, the resultant strain can make the hem area—both the top of the hems and the hem seals—vulnerable to failure during use.
The combination of the strain from the drawstrings and the localized force from the downward pressure of the bag contents can lead to tears or even total failure of the bag in the hem areas. As a result, the top of the hem encompassing the drawstring can often break and/or the linear hem seals at the bottom of the hems may rip apart.
In light of the foregoing, a need exists for improved constructions of drawstring trash bags to enhance the performance of such bags, particularly with respect to the areas around the hems. It would be desirable to provide a drawstring trash bag that can more reliably encompass the bag drawstrings during use. The present invention provides a unique solution to these concerns and may provide other advantages not expressly described herein.